X-ray generating device



Patented oct. 18, 1938 2,133,606

UNITED STATES PATENT OFFICE X-RAY GENERATING DEVICE Jesse` W. M. Du Mond', Pasadena, Calif.

Application April 28, 1937, Serial No. 139,507

6 Claims. (C1. Z50-35) This invention relates to X-ray generating detarget having a relatively high heat capacity vices and pertains particularly to a device prosufficient to permit absorption of the thermal vided with a mobile target andv adapted for suS- energy for a very brief time, the target being tained high power inputv andhighl X-ray output. subsequently cooled over a comparatively pro- 5 One of the particular objects of the invention tracted period in the absence of bombardment 5v is to provide an X-ray generating device probefore a second exposure to the focal spot is vided with-a continuously moving anode surface. made, or have relied upon a rotating struc- A further object of the invention is to provide ture in which vacuum-sealing glands are rea device of the character described, provided quired. This latter conception requires the use' l with an anode member of extended area which of structures in which the sealing surfaces are in 10. is adapted for continuous` movement with referconstant sliding engagement with one another, ence to the cathode whereby the area of the thus limiting the relative rotation of the parts anode which receives electrons from the cathode to slow speeds if a high degree of evacuation of is caused to continuously shift in order to keep the tube is desired. In such constructions, owing l the surface density of electron impingement beto the cooling diiculties, the average safe rate 15 low a desired lmaximumover they entire effective of power input over any protracted time i's very area of thev anode. restricted.

A further object of the invention is to provide The device of the present invention comprises,

a high power X-ray generating device having a essentially, a continuously bombarded movable continuously moving anode surface, in which an target member of extended area mounted in 20 effective vacuum seal may be preserved between such manner as to undergo approximately a cirthe relatively movable parts of the device while cular motion of translation in which anyv parpermitting free effective circulation of a cooling ticular portion of the target is exposed to elecmedium to the anode member. tron bombardment for a short enough period so A further object of the invention is toV provide that that portion does not becomek overheated, 25

an X-ray generating device having a target and is maintained out of exposure to the bomrnember which continuously moves so that new bardment for a sufficient time to become cooled regions of its surface are continuously being prethrough the agency of anv associated fluid or sented under the focal area of electron bomother cooling means before reexposure to the bardment without variation in the position of bombardment, whereby a dynamically steadt7 30 the focal spot with respect to other stationary cyclic thermal state is established in the face objects in the room. of the target, while maintaining the focal spot X-ray generating devices have heretofore been in a fixed position. suggested in which eitherv the foeai spot moves According to the herein disclosed embodiment.

over the face of a stationary target or the tarthe objects of the present invention are attained 35 get surface is moved with respect to a stationby a "OrlstructionY in which theA target member ary focal spot, for the purpose of permitting high iS mOUIlted Orl en elelgeted Support arm which power input over short periods of time. In coniS DlOVided With pivOtai attachment t0 a Xed structions in which the target is stationary and Dertien 0f the tube assembly in Such manuel' the focal spot is caused to move with respect that the aXiS Of the SUDDOIt drm may be CauSed 40 thereto, the adequate cooling of the target pret0 levOlve 01 gylte abOut a Center line intersents` no particular diflculties, but the position Seetillg the eXiS 0f the afm et the DOil'lt 0f DiV- o-f the source of the resulting X-rays is caused Otel support, whereby said axis will be caused to continuously shift which rendersv such cont0 SWeeD Out a COHe having itS aDeX et the Cellstructions substantially useless for many purtel 0f pivOtel SUDDOIt 0f Said arm- The face 0f 45 poses. In constructions where the focal spot is the target iS thus provided With a CiICular and caused to remain motionless and a` continuous nearly telHSletOly mOtOn, WtilOU-t DI'OdUCng an movement of the target is provided, consideractual IOtatiOYi 0f the target member OI SuppOlt able -diiculty has heretofore been experienced in alm- The SUDPOIt erm iS Preferably' eXteIlded providing for continuous andl rapid removal of 100th Sides 0f the Center pivOtal Support to DFO- 5f, the relatively large quantities of heat from the Vide f01" Operative aSSOCiatOn 0f the device With target which result from high kilowatt input. a suitable driving means OI producing the de- As far as is known to applicant all such construcsired revolving motion, and a flexible sealing tions have either involved intermittent bommeans is provided adjacent to the point of pivfj bardment and relied upon the provision of a otal attachment to establishy the desired vacuum seal for the tube. Cooling means are provided for the device, which may conveniently extend within the aforesaid support arm into position to establish positive fluid circulation to the internal rearward surface of the target member as close as possible to the region of electron bombardment.

For the purpose of simplicity of description, the above-described revolving movement of the target member and the associated support mechanism will be referred to as a gyratory movement, in view of the fact that no more accurately descriptive term is available. It is appreciated that the term gyratory is ordinarily applied to the movement of rotating bodies, while in the present case the target and support assembly do not undergo rotation, but in view of the fact that the actual movement which is particularly involved in the operation of the specific form of apparatus herein disclosed for the purpose of providing the desired nearly translatory movement of the target member so closely resembles the movement through Space of a spinning body such as a top, the term gyratory is believed properly descriptive.

Other objects and features of the invention will be brought out in the following description, or will be apparent therefrom. A preferred embodiment of the invention is shown in the accompanying drawing, and referring thereto:

Fig. 1 is a longitudinal section of a complete X-ray tube constructed according to the present invention;

Fig. 2 is a partly fragmentary sectional detail of the cathode, anode, and pivotal mounting construction;

Fig. 2a is a partly diagrammatic representation of the movement of the target member with reference to the focal spot;

Fig. 3 is an enlarged sectional view taken on line 3-3 in Fig. l, showing the construction of a form of driving means which may be employed for producing the desired substantially circular translatory movement of the target face; and

Fig. 4 is an end elevation thereof taken on line 4--4 in Fig. 3.

Referring to the drawing, a tube body portion or envelope is indicated at I, said body portion comprising a center section 2 and two end sections 3 and 4. The end sections 3 and 4 may comprise suitable tubular members such as porcelain insulators secured to the center section 2 in any suitable manner as through the agency of bolted flange constructions as indicated at 5, suitable rubber gaskets or the like being provided between the flanges and the members 3 and 4 as at 6. The cathode assembly 'I is provided with a filament 1a, the cathode assembly being mounted to the end of the portion 3 through the agency of a suitable bolted flange construction 8. The anode assembly is indicated generally at 9, being shown more fully in Figs. 2 and 3.

The anode assembly 9 may comprise a target II secured to a tubular support arm I2 pivotally mounted on a standard I3 which is fixed to the outer end of the member 4. The standard I3 is of tubular construction, and extends within the end section 4 and cooperates with the tube body as a Whole to provide a fixed housing structure, said standard being provided at its inner end with a collar member I4 carrying two diametrically opposed pivot pins I5 adapted to receive a gimbal ring I6. The tubular support arm I2 is provided with diametrically opposed pivot pins I'I adapted to extend within slots I8 in the gimbal ring I6 disposed at positions 90 removed from the positions of the respective pins I5. The pins I'I are preferably secured to a separate sleeve I9 which is soldered or otherwise hermetically attached to the support arm I2. The gimbal ring I6, in conjunction with pins I5 and I'I, serve to mount the support arm I2 for pivotal movement about a point which is conveniently located in the axis of said arm. Hermetic sealing between the interior of the standard I3 and the interior of the body portion I of the tube is provided by flexible sealing means disposed adjacent the point of pivotal support of arm I2 and secured to said arm and to a fixed part of the housing structure, such as standard I3. Such sealing means are shown as comprising a sylphon bellows 2I, one end of which is secured to the collar I4 as at 22 as by means of solder or the like, and the other end of which is secured to a collar 23 which is in turn sealed to the sleeve I9 as by means of coactingly threaded portions 24 which are preferably hermetically sealed as by means of solder.

The standard I3 is flxedly mounted within the outer end of the tube section 4 as by means of a flange 3l, which is preferably welded to the standard I3 to provide a hermetic seal, said flange 3| being bolted as at 32 to a compression flange 33 which is secured to the tube section 4 in any suitable manner as by means of cap screws 34 extending into a reinforcing ring 35 which is cemented or otherwise secured to the tube section 4. A suitable gasket such as of rubber, lead, or the like is provided as at 36 between the outer end of the tube section 4 and the compression flange 33, and a flexible sealing member such as a sylphon bellows 31 is provided between the flanges 3l and 33, the respective ends of which are hermetically sealed to the respective flanges 3l and 33 as by means of soft solder or the like.

When the tube is evacuated to establish the desired operating pressure, the whole of the tube exteriorly of the standard I3 is thus established at the tube pressure (or vacuum) while the interior of the standard I3 is at atmospheric pressure. The double flange construction at 3l and 33 provides for alinement of the standard I3 within the tube, by variation of the direction of the longitudinal axis of the tubular standard I3 with respect to the cathode filament 'Ia through adjustment of the bolts 32, and the desired seal against atmospheric pressure is provided between the flange 33 and the outer end of the tube section 4 through the agency of the bellows 31 as above described.

Any suitable means may be provided for producing the desired gyratory movement of the support arm I2 and thus cause the desired nearly translatory movement of the target face I Ib. In view of the fact that relatively high speeds of gyration are desirable in order to permit a sustained high power input, it is very desirable, if not essential, to provide means for counterbalancing the gyratory assembly. I have illustrated one form of driving means, which is subject to the desired counterbalancing, in which a suitable bearing member 4I such as a ball bearing is mounted on the outer end of the standard I3, said bearing member carrying a grooved pulley 42 to which a driving head 43 is secured. The pulley 42 and the associated driving head 43 are preferably disposed concentric with the standard I3 and radially adjustable connecting means are provided on the head 43 through which the support arm I2 may extend, such adjustable means serving to position the outer end of the support arm I2 at any desired radial displacement from the center of rotation of the head 43, so that upon rotation of the pulley 42 the outer end of the support arm I2 will be given a circular and nearly translatory movement of any desired radius.

The eccentric driving means may comprise a journal bearing 44 slidably and rotatively engaging a sleeve 45 which is disposed about the tubular support arm I-2, being p-referably soldered to the sleeve I9 adjacent the p-oint of pivotal attachment of the arm I2 and standard I3 and soldered or otherwise secured to the arm I2 rearwardly of the head 43 to facilitate assembly of the device and to provide an effective seal between the sleeve I9 and tubular support arm I2.

- The bearing 44 is pivotally mounted on a plate 45 which is slidably secured to the head 43 as by means of suitable dove-tailed guides 4l which provide for adjustment of the plate 46 in a radial direction along the face of head 43. The bearing 44 is pivotally mounted to the plate 46 in any suitable manner as through the agency of diametrically opposed trunnions 48 whose axes lie perpendicular to the direction of adjustment ofthe plate 46. These trunnions are preferably carried in trunnion blocks 49 which are loosely mounted in suitable sockets in the plate 45 and retained in place through the agency of capsy 5I). The loose mounting of the trunnion blocks 49 is desirable in order to prevent the introduction -of any strains due yto slight misalinement of the parts. i

The desirable dynamical counterbalancing of the revolving gyratory assembly may be secured by the disposition of a suitable weight on the rotating assembly in such manner as to counteract the dynamic forces set upby the revolving masses, and for this purpose I provide a balance tube 5I secured to and extending rearwardly of the head 43, on which a suitable counter weight 52 is mounted. The calculation of the forces set up by the gyration of the arm I2 and its accessory elements and the target II, and by rotation of the head 43 carrying the eccentric load of the plate 45, etc., and the proper disposition of the counter weight 52, will be apparent to one skilled in the art.

The target II is preferably provided with cooling means, which may comprise a circulating system for supply of a cooling fluid to the target, such as a water supply tube 55 extending concentrically within the tubular support arm I2 and communicating with a chamber 56 located within the body portion IIa of the target I I, the return circulation of water being effected through the space between the exterior of the tube 55 and the interior Wall of the support arm I2. Fluid connections such as indicated at 51 and 58 in Fig. 1 are pr-ovided for supply and discharge of the cooling fluid, suitable rubber hoses or other flexible conduits being connected thereto.

In the operation of the device a rotation of the pulley 42 at a suitable speed is secured through the agency of a belt drive or the like, causing a gyratory movement of the support arm I2, the radius of gyration being determined by the setting of the plate 46 and the bearing 44 with respect to the center of rotation of the head 43.

The radius of gyration, or, more properly, the half apex angle of the cone of gyration, is such that the radius of the circular path of translation Vof the center of the target face IIb is considerably greater than the radius ofthe' area'v of electron bombardment on the target', so that any particular portion of the target face which is scanned by the electron stream 'isf cyclically exposed to electron bombardment for a relatively short period and is maintained out of electron bombardmentfor a relatively long period. O-wing to the fact that the gimbal ring IE54 and the pins I5 and I'I prevent actualv rotation of the arm I2 with respect to the tube housing, there is no rotative strain placed upon the bellows 2|, said bellows serving to provide the desired vacuum seal between the standard I3 and the arm I2 while permitting free relative angular movement between these parts during the gyrating o r revolving movement of said arm I2.

In Fig. 2a. I have illustrated the target II in full lines corresponding to the full line position thereof shown in Fig. 2 and have shown in dotdash lines at I I and I I" the corresponding positions of thetarget when the support arm has been moved to positions 120 vsuccessively removed from the position shown in fully lines. The electron stream indicated in dot-dash lines at E- in Fig. 2 is fixed in space, and hence the focal spot (where the electron stream impinges upon the target surface) may be caused to be fixed in space (with respect to other stationary objects in the room in which the X-ray tube is located). Due to the nearly translatory movement of the face IIb of the target II, the target -is moved with reference to the focal spot in such manner that said focal spot is swept over an annular surface represented by the shaded ring in Fig. 2a, the focal spot being indicated by tho double cross-hatched circle 26. 'Ihecenter point of the target II is indicated by the dot-dash cross at c, c', and c" for the several positions shown at II, II', and II, and the positions occupied by the focal spot 25 are indicated by the dot-dash circles 26 and 26" within the shaded area 25, showing the eiective progression of the focal spot 26 over the target I I as said target moves through the positions shown at II and II, respectively.

The rate of gyration of the target II will depend upon the power input and the ratio of areas of the focal spot and the annulus traversed thereby, and will in general be so established with respect to a given power input that the circulated cooling fluid will keep the inside wall of the target cool enough so that the heat produced at a given position of the focal spot with respect to the annulus 25 will be conducted away from the outer surface of the target in one gyration of the target assembly, without exceeding safe values of temperature on the target surface, i. e., by the time the focal spot is again impinging upon the same portion of the target. It will be appreciated that focal spots are not uniform over their entire area, due to the emission characteristics of the cathode filament, and local hot spots are Very frequently present. For this reason the target is preferably gyrated at a somewhat faster rate than that theoretically called for by a focal spot which is uniformly loaded, to provide a factor of safety. VThe theoreticaly considerations and mathematical treatment of the thermal problem involved in X-ray assemblies which provide a mobile focal spot either b-y actual movement of the anode or by movement of the cathode, are set forth in July 1935 issue of the Review of Scientific Instruments, published by the American Institute of Physics, of which I am a co-author. 1

The tube sections 3 and 4 are above described as of porcelain, and the tube body is formed in three sections. It will be appreciated that this construction is not essential to the invention and was merely a matter of practical expediency in the actual construction of thel device, in which ready assembly and dismounting of the structure was desirable. It will be comprehended that the tube body may be formed as an integral envelope, of glass or other suitable material. The device is preferably provided with adequate shielding means whereby only such X-rays as are to be used are allowed to escape from the envelope, such shielding means being indicated about the cathode-anode assembly in Fig. 2, and a suitable aperture 21 being left in a portion of the shielding which encompasses the center section 2 to serve as a window for the useful X-rays. Similarly, in order to prevent escape of X-rays through the end of the tube, as well as to prevent undue heating of the soldered joints located adjacent to the pivotal mounting of the arm I2, I preferably provide an annular lead shield 28 about the arm I2 forwardly of such pivotal mounting, said shield being conveniently carried onV the standard I3 through the agency of an extension 29 secured thereto. Fig. 1 also illustrates the provision of a diffusion pump for maintaining the desired condition. of reduced pressure within the tube body, and under some circumstances I prefer to use a suitable adsorbing medium such as a charcoal tra-p for the purpose of adsorbing vapors which may be emitted from the gasket material or the diffusion pump. The electrical connections to the cathode filament and to the anode are in accordance with the conventional practice in the art.

The length of the support arm I2 from the center of pivotal support thereof to the target face IIb is preferably so selected with respect to the extent of translatory movement required at the target face that the angle which the target face makes with the electron stream E does not vary to a large extent, although said target face may conveniently be formed as a spherical cap whose center is located at the pivotal center of the arm I2. The use of a small apical angle of the cone swept out in the gyrating movement also avoids excessive reversing stresses on the bellows 2|, thus lengthening its life before failure by fatigue.

While I have delineated but a single form of pivotal mounting for the anode support arm I2 and a single form of driving means for producing the desired nearly circular translatory movement of the target face, it will be apparent to one skilled in the art that modifications may be made in these specific considerations Without departing from the spirit and contemplation of the invention. It will further be appreciated that the device may be caused to extend vertically, or at any other desired angle to the horizontal, depending upon the particular construction desired. When particularly heavy target structures are employed, it may be desirable to dispose the axis of the target support arm in a generally vertical direction, whereby the translatory motion produced in the target will be more symmetrical owing to the absence of distorting forces resulting from the force of gravity.

I claim:

1. An X-ray generating device which comprises: an evacuated envelope; a tubular standard secured to said envelope and extending interiorly thereof, said tubular standard cooperating with said evacuated envelope to define a housing structure for said device; a target member disposed within said envelope; an elongated target support arm carrying said target member and pivotally secured to said standard at a point outwardly removed from said target member; ilexible metallic sealing means hermetically secured to said standard and said support arm adjacent the point of pivotal attachment of said support arm; a cathode member disposed within said envelope and adapted to produce a stream of electrons directed toward and against said target member; driving means for producing gyratory movement of said support arm to cause the axis thereof to describe a cone having its apex at the center of pivotal support of said arm and thereby cause said target to undergo approximately a circular motion of translation, in the absence of actual rotation, while remaining in position to receive said electron stream, whereby the focal spot produced by said electron stream on said target is caused to describe a cyclic path on the surface of the target; and fluid circulating means associated with said target member for conducting heat therefrom.

2. An X-ray generating device which comprises: an elongated envelope; a tubular standard secured to said envelope adjacent one end thereof and extending interiorly thereof in the direction of the length of said envelope; a target member disposed within said envelope; an elongated target support arm carrying said target member and extending within said tubular standard; pivotal supporting means for said support arm mounted on said tubular standard adjacent the inner end thereof; flexible sealing means disposed adjacent said pivotal supporting means and connected to said tubular standard and to said support arm and cooperating with said envelope and said tubular standard and support arm to seal the interior of said envelope from the atmosphere and from the space Within said tubular standard; a cathode member disposed within said envelope and adapted to produce a stream of electrons directed toward and against said target member; driving means for producing gyratory movement of said support arm to cause the axis thereof to describe a cone having its apex at the center of pivotal support of said arm and thereby cause said target to undergo approximately a circular motion of translation, in the absence of actual rotation, While remaining in position to receive said electron stream, whereby the focal spot produced by said electron stream on said target is caused to describe a cyclic path on the surface of the target; and fluid circulating means associated with said target member for conducting heat therefrom.

3. The structure set forth in claim 2, and comprising in addition, counterbalancing means associated with said driving means and located exteriorly of said envelope in position to establish a dynamic balance in said driving means and said elongated target support arm.

4. An X-ray generating device which comprises: an evacuated envelope; a tubular standard secured to said envelope and extending interiorly thereof, said tubular standard cooperating with said evacuated envelope to define a housing structure for said device; a target member disposed within said envelope; an elongated target support arm carrying said target member and pivotally secured to said standard at a point outwardly removed from said target member; flexible metallic sealing means hermetically secured to said standard and said support arm adjacent the point of pivotal attachment of said support arm; a cathode member disposed within said envelope and adapted to produce a stream of electrons directed toward and against said target member; driving means for producing gyratory movement of said support arm to cause the axis thereof to describe a cone having its apex at the center of pivotal support of said arm and thereby cause said target to undergo approximately a circular motion of translation, in the absence of actual rotation, while remaining in position to receive said electron stream, whereby the focal spot produced by said electron stream on said target is caused to describe a cyclic path on the surface of the target; fluid circulating means associated with said target member for conducting heat therefrom; and means for varying the direction of the longitudinal axis of said tubular standard with respect to the position of said cathode member and including a flexible metallic sealing member hermetically secured to said standard and to said envelope at the position of attachment of said standard to said envelope.

5. An X-ray generating device which comprises: an evacuated envelope; a tubular standard secured to said envelope and extending interiorly thereof, said tubular standard cooperating with said evacuated envelope to define a housing structure for said device; a target member disposed within said envelope; an elongated target support arm carrying said target member and pivotally secured to said standard at a point outwardly removed from said target member; flexible metallic sealing means hermetically secured to said standard and said support arm adjacent the point of pivotal attachment of said support arm; a cathode member disposed within said envelope and adapted to produce a stream of electrons directed toward and against said target member; driving means for producing gyratory movement of said support arm to cause the axis thereof to describe a cone having its apex at the center of pivotal support of said armand thereby cause said target to undergo approximately a circular motion of translation, in the absence of actual rotation, While remaining in position to receive said electron stream, whereby the focal spot produced by said electron stream on said target is caused to describe a cyclic path on the surface of the target; and iiuid circulating means associated with said target member for conducting heat therefrom, said driving means comprising driving head means rotatably secured to said housing structure adjacent the outer end of said tubular standard and provided with a. radially adjustable journal bearing in rotative sliding engagement with said elongated target support arm.

6. An X-ray generating device which comprises: an evacuated envelope; a tubular standard secured to said envelope and extending interiorly thereof, said tubular standard cooperating with said evacuated envelope to define a housing structure for said device; a target member disposed within said envelope; an elongated target support arm carrying said target member and pivotally secured to said standard at a point outwardly removed from said target member; flexible metallic sealing means hermetically secured to said standard and said support arm adjacent the point of pivotal attachment of said support arm; a cathode member disposed Within said envelope and adapted to produce a stream of electrons directed toward and against said target member; driving means for producing gyratory movement of said support arm to cause the axis thereof to describe a cone having its apex at the center of pivotal support of said arm and thereby cause said target to undergo approximately a circular motion of translation, in the absence of actual rotation, While remaining in position to receive said electron stream, whereby the focal spot produced by said electron stream on said target is caused to describe a cyclic path on the surface of the target, said driving means comprising driving head means rotatably secured to said housing structure adjacent the outer end of said tubular standard and provided with a radially adjustable journal bearing in rotative sliding engagement with said elongated target support arm; counterbalancing means secured to said driving head means in position to establish a dynamic balance in the rotative and gyratory portions of said device; and fluid circulating means associated'with said target member for conducting heat therefrom.

JESSE W. M. DU MOND. 

